A higher than expected prevalence of AVNRT in patients receiving implantable defibrillators

Abstract

The prevalence of paroxysmal supraventricular tachycardia (SVT) is approximately 2-3/1000, of whom 50–60% have AV nodal reentrant tachycardia (AVNRT). Inappropriate shocks for SVT are reported in 17–41% of ICD patients. To characterize the prevalence of AVNRT in patients with an ICD, charts of patients implanted and followed since 1994 were reviewed for pre-implant history of AVNRT, inducible AVNRT at pre-implant electrophysiology study (EPS) and for clinical episodes of AVNRT (confirmed by EPS) post-implant. There were 648 implants. Of 426 patients followed, a total of 15 patients with AVNRT were identified (3.5%). Mean age was 54±16 years with 9 males. Mean ejection fraction was 32±18%. ICD indications were ischemic (n=6), nonischemic (n=5),or hypertrophic (n=2) cardiomyopathy, and congenital heart disease (n=2). These characteristics did not differ from the total ICD population. AVNRT was noted pre-implant in 9 patients. One had remote AVNRT and had undergone RF ablation (RFA). Four patients had known clinical episodes of SVT; 3/4 underwent RFA prior to ICD implant. Four patients had AVNRT induced at pre-implant EPS (cycle length 409±81 ms) and 3 had RFA prior to ICD implant. Seven patients had clinical episodes of AVNRT after ICD implant, cycle length 360±39 ms; 6/7 received ICD therapy for AVNRT (of a total 44 patients who received ICD therapy for all types of SVT). All 7 had RFA for AVNRT. Of the 14 patients who had AVNRT induced at EPS, cycle length was 367±78 ms, range 240–485 ms. No patient who underwent RFA had further clinical episodes of SVT and only one had further inappropriate ICD therapy for sinus tachycardia. There is a substantially higher prevalence of AVNRT in our ICD population (3.5%) than in the general population. This may reflect a detection bias due to performing EPS and/or extended arrhythmia monitoring by the ICD. Alternatively, electroanatomic changes in the AV nodal area induced by the accompanying heart disease in these patients may predispose to AVNRT. AVNRT accounts for a significant percentage (13.6%) of inappropriate therapy for SVT. Further studies to evaluate AVNRT inducibility prior to ICD implant and its implications are warranted.